Nonvolatile charge trap memory device having a high dielectric constant blocking region

ABSTRACT

A nonvolatile charge trap memory device is described. The device includes a substrate having a channel region and a pair of source and drain regions. A gate stack is above the substrate over the channel region and between the pair of source and drain regions. The gate stack includes a high dielectric constant blocking region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/007,566, filed Dec. 12, 2007, the entire contents of which are hereby incorporated by reference herein.

TECHNICAL FIELD

The invention is in the field of Semiconductor Devices.

BACKGROUND

For the past several decades, the scaling of features in integrated circuits has been a driving force behind an ever-growing semiconductor industry. Scaling to smaller and smaller features enables increased densities of functional units on the limited real estate of semiconductor chips. For example, shrinking transistor size allows for the incorporation of an increased number of memory devices on a chip, lending to the fabrication of products with increased capacity. The drive for ever-more capacity, however, is not without issue. The necessity to optimize the performance of each device becomes increasingly significant.

Non-volatile semiconductor memories typically use stacked floating gate type field-effect-transistors. In such transistors, electrons are injected into a floating gate of a memory cell to be programmed by biasing a control gate and grounding a body region of a substrate on which the memory cell is formed. An oxide-nitride-oxide (ONO) stack is used as either a charge storing layer, as in a semiconductor-oxide-nitride-oxide-semiconductor (SONOS) transistor, or as an isolation layer between the floating gate and control gate, as in a split gate flash transistor. FIG. 1 illustrates a cross-sectional view of a conventional nonvolatile charge trap memory device.

Referring to FIG. 1, semiconductor device 100 includes a SONOS gate stack 104 including a conventional ONO portion 106 formed over a silicon substrate 102. Semiconductor device 100 further includes source and drain regions 110 on either side of SONOS gate stack 104 to define a channel region 112. SONOS gate stack 104 includes a poly-silicon gate layer 108 formed above and in contact with ONO portion 106. Poly-silicon gate layer 108 is electrically isolated from silicon substrate 102 by ONO portion 106. ONO portion 106 typically includes a tunnel oxide layer 106A, a nitride or oxy-nitride charge-trapping layer 106B, and a top oxide layer 106C overlying nitride or oxy-nitride layer 106B.

One problem with conventional SONOS transistors is the limited program and erase window achievable with a conventional blocking layer 106C, inhibiting optimization of semiconductor device 100. For example, FIG. 2 is a plot 200 of Threshold Voltage (V) as a function of Pulse Width (s) in erase mode for a conventional nonvolatile charge trap memory device. Referring to FIG. 2, line 202 is a measure of decreasing threshold voltage (in Volts) as a function of time (in seconds) in response to an erase-mode voltage being applied to a gate electrode in a conventional SONOS transistor. As indicated by region 204 of line 202, the ability of the erase mode to decrease the threshold voltage of the gate electrode saturates with time, restricting an erase event to a relatively shallow erase of the gate electrode. The shallow erase limits the differential between erase and program modes for a SONOS-transistor and thus limits the performance of such a device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of a conventional nonvolatile charge trap memory device.

FIG. 2 is a plot of Threshold Voltage (V) as a function of Pulse Width (s) in erase mode for a conventional nonvolatile charge trap memory device.

FIG. 3 is a plot of Threshold Voltage (V) as a function of Pulse Width (s) in erase mode for a nonvolatile charge trap memory device having a high dielectric constant blocking region, in accordance with an embodiment of the present invention.

FIG. 4 is a plot of Charging Current (A/cm²) as a function of Gate Voltage (V) for four different nonvolatile charge trap memory devices, in accordance with an embodiment of the present invention.

FIG. 5 illustrates a cross-sectional view of a nonvolatile charge trap memory device having a multi-layer high dielectric constant blocking region, in accordance with an embodiment of the present invention.

FIG. 6 illustrates a cross-sectional view of a nonvolatile charge trap memory device having a graded high dielectric constant blocking layer, in accordance with an embodiment of the present invention.

FIG. 7A illustrates a cross-sectional view representing an operation in the formation of a nonvolatile charge trap memory device having a multi-layer high dielectric constant blocking region, in accordance with an embodiment of the present invention.

FIG. 7B illustrates a cross-sectional view representing an operation in the formation of a nonvolatile charge trap memory device having a multi-layer high dielectric constant blocking region, in accordance with an embodiment of the present invention.

FIG. 7C illustrates a cross-sectional view representing an operation in the formation of a nonvolatile charge trap memory device having a multi-layer high dielectric constant blocking region, in accordance with an embodiment of the present invention.

FIG. 7D illustrates a cross-sectional view representing an operation in the formation of a nonvolatile charge trap memory device having a multi-layer high dielectric constant blocking region, in accordance with an embodiment of the present invention.

FIG. 7E illustrates a cross-sectional view representing an operation in the formation of a nonvolatile charge trap memory device having a multi-layer high dielectric constant blocking region, in accordance with an embodiment of the present invention.

FIG. 7F illustrates a cross-sectional view representing an operation in the formation of a nonvolatile charge trap memory device having a multi-layer high dielectric constant blocking region, in accordance with an embodiment of the present invention.

FIG. 7G illustrates a cross-sectional view representing an operation in the formation of a nonvolatile charge trap memory device having a multi-layer high dielectric constant blocking region, in accordance with an embodiment of the present invention.

FIG. 7H illustrates a cross-sectional view representing an operation in the formation of a nonvolatile charge trap memory device having a multi-layer high dielectric constant blocking region, in accordance with an embodiment of the present invention.

FIG. 7I illustrates a cross-sectional view representing an operation in the formation of a nonvolatile charge trap memory device having a multi-layer high dielectric constant blocking region, in accordance with an embodiment of the present invention.

FIG. 8A illustrates a cross-sectional view representing an operation in the formation of a nonvolatile charge trap memory device having a graded high dielectric constant blocking layer, in accordance with an embodiment of the present invention.

FIG. 8B illustrates a cross-sectional view representing an operation in the formation of a nonvolatile charge trap memory device having a graded high dielectric constant blocking layer, in accordance with an embodiment of the present invention.

FIG. 8C illustrates a cross-sectional view representing an operation in the formation of a nonvolatile charge trap memory device having a graded high dielectric constant blocking layer, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

A nonvolatile charge trap memory device and a method to form the same is described herein. In the following description, numerous specific details are set forth, such as specific dimensions, in order to provide a thorough understanding of the present invention. It will be apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known processing steps, such as patterning steps or wet chemical cleans, are not described in detail in order to not unnecessarily obscure the present invention. Furthermore, it is to be understood that the various embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale.

Disclosed herein is a nonvolatile charge trap memory device. The device may include a substrate having a channel region and a pair of source and drain regions. A gate stack may be formed above the substrate over the channel region and between the pair of source and drain regions. In an embodiment, the gate stack includes a high dielectric constant blocking region. In one embodiment, the high dielectric constant blocking region is a bi-layer blocking dielectric region having a first dielectric layer disposed directly above a charge-trapping layer and a second dielectric layer disposed directly above the first dielectric layer and directly below a gate layer. The dielectric constant of the first dielectric layer is lower than the dielectric constant of the second dielectric layer. In another embodiment, the high dielectric constant blocking region is a graded blocking dielectric layer disposed directly above a charge-trapping layer and directly below a gate layer. The dielectric constant of the graded blocking dielectric layer has a low-to-high gradient in the direction from the charge-trapping layer to the gate layer.

A nonvolatile charge trap memory device including a high dielectric constant blocking region may exhibit a relatively large program and erase window, enabling improved performance of such a device. For example, in accordance with an embodiment of the present invention, FIG. 3 is a plot 300 of Threshold Voltage (V) as a function of Pulse Width (s) in erase mode for a nonvolatile charge trap memory device having a high dielectric constant blocking region. Referring to FIG. 3, line 302 is a measure of decreasing threshold voltage (in Volts) as a function of time (in seconds) in response to an erase-mode voltage being applied to a gate electrode in a nonvolatile charge trap memory transistor. As indicated by region 304 of line 302, the ability of the erase mode to decrease the threshold voltage of the gate electrode does not substantially saturate with time, allowing for a relatively deep erase of the gate electrode. In one embodiment, the deep erase enables a greater differential between erase and program modes for a nonvolatile charge trap memory transistor.

The ability to achieve a deep erase in a nonvolatile charge trap memory device including a high dielectric constant blocking region may result from the ability of the high dielectric constant blocking region to mitigate back-streaming of electrons. Such back-streaming otherwise proceeds into a charge-trapping layer that is subject to an erase-mode voltage application. For example, in accordance with an embodiment of the present invention, FIG. 4 is a plot 400 of Charging Current (A/cm²) as a function of Gate Voltage (V) for four different nonvolatile charge trap memory devices. Referring to FIG. 4, lines 402, 404, 406 and 408 are measures of increasing charging current (“back-streaming” in Amperes per square centimeter) as a function of gate voltage (in Volts) in response to an erase-mode voltage being applied to gate electrodes in a series of four nonvolatile charge trap memory transistors, respectively. Lines 402, 404, 406 and 408 represent data obtained from nonvolatile charge trap memory transistors having progressively physically thicker blocking dielectric layers, respectively, but all having approximately the same equivalent oxide thickness (EOT), i.e. the same electrical thickness. In one embodiment, the amount of gate voltage required to produce a significant back-streaming event increases with increasing physical thickness of the blocking dielectric layer, as depicted in FIG. 4. Thus, in a specific embodiment, the higher the dielectric constant of the blocking dielectric layer, the less back-streaming observed at a given voltage and at a given electrical thickness. In comparison with a conventional memory device, the reduction in back-streaming may enable a greater program and erase window, improving the performance of a nonvolatile charge trap memory device at a given electrical thickness. However, the same effect may be exploited to scale down the electrical parameters of a nonvolatile charge trap memory device. For example, in accordance with an alternative embodiment of the present invention, a high dielectric constant blocking region has a smaller EOT than the blocking layer of a conventional memory device. In a specific alternative embodiment, a high dielectric constant blocking region has a smaller EOT than the blocking layer of a conventional memory device, and a nonvolatile charge trap memory device incorporating the high dielectric constant blocking region is operated at a lower gate voltage than the gate voltage used for the conventional memory device.

A nonvolatile charge trap memory device may include a multi-layer blocking dielectric region. FIG. 5 illustrates a cross-sectional view of a nonvolatile charge trap memory device having a multi-layer high dielectric constant blocking region, in accordance with an embodiment of the present invention.

Referring to FIG. 5, semiconductor device 500 includes a gate stack 504 formed over a substrate 502. Semiconductor device 500 further includes source and drain regions 510 in substrate 502 on either side of gate stack 504, defining a channel region 512 in substrate 502 underneath gate stack 504. Gate stack 504 includes a tunnel dielectric layer 504A, a charge-trapping layer 504B, a multi-layer blocking dielectric region 504C, and a gate layer 504D. Thus, gate layer 504D is electrically isolated from substrate 502. Multi-layer blocking dielectric region 504C includes a first dielectric layer 506 disposed above charge-trapping layer 504B and a second dielectric layer 508 disposed above first dielectric layer 506 and below gate layer 504D. A pair of dielectric spacers 514 isolates the sidewalls of gate stack 504.

Semiconductor device 500 may be any nonvolatile charge trap memory device. In one embodiment, semiconductor device 500 is a Flash-type device wherein the charge-trapping layer is a conductor layer or a semiconductor layer. In accordance with another embodiment of the present invention, semiconductor device 500 is a SONOS-type device wherein the charge-trapping layer is an insulator layer. By convention, SONOS stands for “Semiconductor-Oxide-Nitride-Oxide-Semiconductor,” where the first “Semiconductor” refers to the channel region material, the first “Oxide” refers to the tunnel dielectric layer, “Nitride” refers to the charge-trapping dielectric layer, the second “Oxide” refers to the blocking dielectric layer and the second “Semiconductor” refers to the gate layer. A SONOS-type device, however, is not limited to these specific materials, as described below.

Substrate 502 and, hence, channel region 512, may be composed of any material suitable for semiconductor device fabrication. In one embodiment, substrate 502 is a bulk substrate composed of a single crystal of a material which may include, but is not limited to, silicon, germanium, silicon-germanium or a III-V compound semiconductor material. In another embodiment, substrate 502 includes a bulk layer with a top epitaxial layer. In a specific embodiment, the bulk layer is composed of a single crystal of a material which may include, but is not limited to, silicon, germanium, silicon-germanium, a III-V compound semiconductor material and quartz, while the top epitaxial layer is composed of a single crystal layer which may include, but is not limited to, silicon, germanium, silicon-germanium and a III-V compound semiconductor material. In another embodiment, substrate 502 includes a top epitaxial layer on a middle insulator layer which is above a lower bulk layer. The top epitaxial layer is composed of a single crystal layer which may include, but is not limited to, silicon (i.e. to form a silicon-on-insulator (SOI) semiconductor substrate), germanium, silicon-germanium and a III-V compound semiconductor material. The insulator layer is composed of a material which may include, but is not limited to, silicon dioxide, silicon nitride and silicon oxy-nitride. The lower bulk layer is composed of a single crystal which may include, but is not limited to, silicon, germanium, silicon-germanium, a III-V compound semiconductor material and quartz. Substrate 502 and, hence, channel region 512, may include dopant impurity atoms. In a specific embodiment, channel region 512 is doped P-type and, in an alternative embodiment, channel region 512 is doped N-type.

Source and drain regions 510 in substrate 502 may be any regions having opposite conductivity to channel region 512. For example, in accordance with an embodiment of the present invention, source and drain regions 510 are N-type doped regions while channel region 512 is a P-type doped region. In one embodiment, substrate 502 and, hence, channel region 512, is composed of boron-doped single-crystal silicon having a boron concentration in the range of 1×10¹⁵-1×10¹⁹ atoms/cm³. Source and drain regions 510 are composed of phosphorous- or arsenic-doped regions having a concentration of N-type dopants in the range of 5×10¹⁶-5×10¹⁹ atoms/cm³. In a specific embodiment, source and drain regions 510 have a depth in substrate 502 in the range of 80-200 nanometers. In accordance with an alternative embodiment of the present invention, source and drain regions 510 are P-type doped regions while channel region 512 is an N-type doped region.

Tunnel dielectric layer 504A may be any material and have any thickness suitable to allow charge carriers to tunnel into the charge-trapping layer under an applied gate bias while maintaining a suitable barrier to leakage when the device is unbiased. In one embodiment, tunnel dielectric layer 504A is formed by a thermal oxidation process and is composed of silicon dioxide or silicon oxy-nitride, or a combination thereof. In another embodiment, tunnel dielectric layer 504A is formed by chemical vapor deposition or atomic layer deposition and is composed of a dielectric layer which may include, but is not limited to, silicon nitride, aluminum oxide, hafnium oxide, zirconium oxide, hafnium silicate, zirconium silicate, hafnium oxy-nitride, hafnium zirconium oxide and lanthanum oxide. In another embodiment, tunnel dielectric layer 504A is a bi-layer dielectric region including a bottom layer of a material such as, but not limited to, silicon dioxide or silicon oxy-nitride and a top layer of a material which may include, but is not limited to, silicon nitride, aluminum oxide, hafnium oxide, zirconium oxide, hafnium silicate, zirconium silicate, hafnium oxy-nitride, hafnium zirconium oxide and lanthanum oxide. Thus, in one embodiment, tunnel dielectric layer 504A includes a high-K dielectric portion. In a specific embodiment, tunnel dielectric layer 504A has a thickness in the range of 1-10 nanometers.

Charge-trapping layer may be any material and have any thickness suitable to store charge and, hence, raise the threshold voltage of gate stack 504. In accordance with an embodiment of the present invention, charge-trapping layer 504B is formed by a chemical vapor deposition process and is composed of a dielectric material which may include, but is not limited to, stoichiometric silicon nitride, silicon-rich silicon nitride and silicon oxy-nitride. In one embodiment, charge-trapping layer 504B is composed of a bi-layer silicon oxy-nitride region. For example, in a specific embodiment, charge-trapping layer 504B includes an oxygen-rich portion and a silicon-rich portion and is formed by depositing an oxygen-rich oxy-nitride film by a first composition of gases and, subsequently, depositing a silicon-rich oxy-nitride film by a second composition of gases. In a particular embodiment, charge-trapping layer 504B is formed by modifying the flow rate of ammonia (NH₃) gas, and introducing nitrous oxide (N₂O) and dichlorosilane (SiH₂Cl₂) to provide the desired gas ratios to yield first an oxygen-rich oxy-nitride film and then a silicon-rich oxy-nitride film. In one embodiment, charge-trapping layer 504B has a thickness in the range of 5-10 nanometers. In accordance with an alternative embodiment of the present invention, charge-trapping layer 504B has a graded composition.

Multi-layer blocking dielectric region 504C may be composed of any material and have any thickness suitable to maintain a barrier to charge leakage without significantly decreasing the capacitance of gate stack 504. In accordance with an embodiment of the present invention, multi-layer blocking dielectric region 504C is a bi-layer blocking dielectric region having a first dielectric layer 506 disposed directly above charge-trapping layer 504B and having a second dielectric layer 508 disposed directly above first dielectric layer 506 and directly below gate layer 504D. In an embodiment, first dielectric layer 506 has a large barrier height while second dielectric layer 508 has a high dielectric constant. In one embodiment, the barrier height of first dielectric layer 506 is at least approximately 2 electron Volts (eV). In a specific embodiment, the barrier height of first dielectric layer 506 is at least approximately 3 eV. In an embodiment, the dielectric constant of first dielectric layer 506 is lower than the dielectric constant of second dielectric layer 508. In one embodiment, first dielectric layer 506 of bi-layer blocking dielectric region 504C is composed of silicon dioxide and second dielectric layer 508 is composed of silicon nitride. In another embodiment, first dielectric layer 506 of bi-layer blocking dielectric region 504C is composed of silicon dioxide and second dielectric layer 508 is composed of a material such as, but not limited to, aluminum oxide, hafnium oxide, zirconium oxide, hafnium silicate, zirconium silicate, hafnium oxy-nitride, hafnium zirconium oxide or lanthanum oxide. In a specific embodiment, first dielectric layer 506 of bi-layer blocking dielectric region 504C is composed of a material having a dielectric constant approximately in the range of 3.5-4.5 and second dielectric layer 508 is composed of a material having a dielectric constant above approximately 7. In accordance with an embodiment of the present invention, multi-layer blocking dielectric region 504C is formed in part by a chemical vapor deposition process. In one embodiment, multi-layer blocking dielectric region 504C is formed from at least two different materials. In a specific embodiment, forming multi-layer blocking dielectric region 504C from at least two different materials includes oxidizing a top portion of charge-trapping layer 504B and, subsequently, depositing a dielectric layer above the oxidized portion of charge-trapping layer 504B. In another specific embodiment, forming graded blocking dielectric layer 504C from at least two different materials includes depositing a first dielectric layer having a first dielectric constant and, subsequently, depositing a second dielectric layer having a second dielectric constant, wherein the second dielectric constant is greater than the first dielectric constant. In a particular embodiment, the first dielectric layer has a thickness approximately in the range of 0.5-3 nanometers, the second dielectric layer has a thickness approximately in the range of 2-5 nanometers, and the first and second dielectric layers are not inter-mixed. Thus, in accordance with an embodiment of the present invention, multi-layer blocking dielectric region 504C has an abrupt interface between first dielectric layer 506 and second dielectric layer 508, as depicted in FIG. 5.

Gate layer 504D may be composed of any conductor or semiconductor material suitable for accommodating a bias during operation of a SONOS-type transistor. In accordance with an embodiment of the present invention, gate layer 504D is formed by a chemical vapor deposition process and is composed of doped poly-crystalline silicon. In another embodiment, gate layer 504D is formed by physical vapor deposition and is composed of a metal-containing material which may include, but is not limited to, metal nitrides, metal carbides, metal silicides, hafnium, zirconium, titanium, tantalum, aluminum, ruthenium, palladium, platinum, cobalt and nickel. In one embodiment, gate layer 504D is a high work-function gate layer.

In another aspect of the present invention, a nonvolatile charge trap memory device may include a graded blocking dielectric layer. FIG. 6 illustrates a cross-sectional view of a nonvolatile charge trap memory device having a graded high dielectric constant blocking layer, in accordance with an embodiment of the present invention.

Referring to FIG. 6, semiconductor device 600 includes a gate stack 604 formed over a substrate 602. Semiconductor device 600 further includes source and drain regions 610 in substrate 602 on either side of gate stack 604, defining a channel region 612 in substrate 602 underneath gate stack 604. Gate stack 604 includes a tunnel dielectric layer 604A, a charge-trapping layer 604B, a graded blocking dielectric layer 604C, and a gate layer 604D. Thus, gate layer 604D is electrically isolated from substrate 602. A pair of dielectric spacers 614 isolates the sidewalls of gate stack 604.

Semiconductor device 600 may be any semiconductor device described in association with semiconductor device 500 from FIG. 5. Substrate 602, source and drain regions 610 and channel region 612 may be composed of any material and dopant impurity atoms described in association with substrate 502, source and drain regions 510 and channel region 512, respectively, from FIG. 5. Tunnel dielectric layer 604A, charge-trapping layer 604B and gate layer 604D may be composed of any material described in association with tunnel dielectric layer 504A, charge-trapping layer 504B and gate layer 504D, respectively, from FIG. 5.

However, in contrast to semiconductor device 500, semiconductor device 600 includes a graded blocking dielectric layer 604C, as depicted in FIG. 6. In accordance with an embodiment of the present invention, graded blocking dielectric layer 604C is disposed directly above charge-trapping layer 604B and directly below gate layer 604D. In an embodiment, the portion of graded blocking dielectric layer 604C directly adjacent to charge-trapping layer 604B has a large barrier height while the portion of graded blocking dielectric layer 604C directly adjacent to gate layer 604D has a high dielectric constant. In one embodiment, the barrier height of the portion of graded blocking dielectric layer 604C directly adjacent to charge-trapping layer 604B is at least approximately 2 eV. In a specific embodiment, the barrier height of the portion of graded blocking dielectric layer 604C directly adjacent to charge-trapping layer 604B is at least approximately 3 eV. In an embodiment, the dielectric constant of graded blocking dielectric layer 604C has a low-to-high gradient in the direction from charge-trapping layer 604B to gate layer 604D. In one embodiment, the portion of graded blocking dielectric layer 604C directly adjacent to charge-trapping layer 604B is composed substantially of silicon dioxide and the portion of graded blocking dielectric layer 604C directly adjacent to gate layer 604D is composed substantially of silicon nitride. In another embodiment, the portion of graded blocking dielectric layer 604C directly adjacent to charge-trapping layer 604B is composed substantially of silicon dioxide and the portion of graded blocking dielectric layer 604C directly adjacent to gate layer 604D is composed substantially of a material such as, but not limited to, aluminum oxide, hafnium oxide, zirconium oxide, hafnium silicate, zirconium silicate, hafnium oxy-nitride, hafnium zirconium oxide or lanthanum oxide. In a specific embodiment, the portion of graded blocking dielectric layer 604C directly adjacent to charge-trapping layer 604B is composed substantially of a material having a dielectric constant approximately in the range of 3.5-4.5 and the portion of graded blocking dielectric layer 604C directly adjacent to gate layer 604D is substantially composed of a material having a dielectric constant above approximately 7. In accordance with an embodiment of the present invention, graded blocking dielectric layer 604C is formed in part by a chemical vapor deposition process. In one embodiment, graded blocking dielectric layer 604C is formed from at least two different materials. In a specific embodiment, forming graded blocking dielectric layer 604C from at least two different materials includes oxidizing a top portion of charge-trapping layer 604B and, subsequently, depositing a dielectric layer above the oxidized portion of charge-trapping layer 604B. In another specific embodiment, forming graded blocking dielectric layer 604C from at least two different materials includes depositing a first dielectric layer having a first dielectric constant and, subsequently, depositing a second dielectric layer having a second dielectric constant, wherein the second dielectric constant is greater than the first dielectric constant. In a particular embodiment, the first dielectric layer has a thickness approximately in the range of 0.5-3 nanometers, the second dielectric layer has a thickness approximately in the range of 2-5 nanometers, and the first and second dielectric layers are then inter-mixed. In one embodiment, the first and second dielectric layers are inter-mixed upon deposition of the second dielectric layer on the first dielectric layer. In another embodiment, the first and second dielectric layers are inter-mixed in an anneal process subsequent to the formation of the first and second dielectric layers. Thus, in accordance with an embodiment of the present invention, there is no distinct interface within graded blocking dielectric layer 604C, as depicted in FIG. 6.

A nonvolatile charge trap memory device may be fabricated to include a multi-layer blocking dielectric region. FIGS. 7A-7I illustrate cross-sectional views representing operations in the formation of a nonvolatile charge trap memory device having a multi-layer high dielectric constant blocking region, in accordance with an embodiment of the present invention.

Referring to FIG. 7A, a substrate 702 is provided. Substrate 702 may be composed of any material and have any characteristics described in association with substrate 502 from FIG. 5. Referring to FIG. 7B, a tunnel dielectric layer 720 is formed on the top surface of substrate 702. Tunnel dielectric layer 720 may be formed from any material, from any process, and have any thickness described in association with tunnel dielectric layer 504A from FIG. 5. Referring to FIG. 7C, a charge-trapping 722 is formed on the top surface of tunnel dielectric layer 720. Charge-trapping layer 722 may be formed from any material, from any process, and have any thickness described in association with charge-trapping layer 504B from FIG. 5.

Referring to FIG. 7D, a multi-layer blocking dielectric region 724 is formed on the top surface of charge-trapping layer 722. Multi-layer blocking dielectric region 724 includes a first dielectric layer 726 disposed above charge-trapping layer 722 and a second dielectric layer 728 disposed above first dielectric layer 726. In accordance with an embodiment of the present invention, multi-layer blocking dielectric region 724 is a bi-layer blocking dielectric region and includes a first dielectric layer 726 and a second dielectric layer 728, as depicted in FIG. 7D. First dielectric layer 726 and second dielectric layer 728 may be formed by any technique, composed of any materials, and have any thicknesses described in association with first dielectric layer 506 and second dielectric layer 508, respectively, from FIG. 5. In accordance with an embodiment of the present invention, multi-layer blocking dielectric region 724 has an abrupt interface between first dielectric layer 726 and second dielectric layer 728, as depicted in FIG. 7D. In one embodiment, multi-layer blocking dielectric region 724 is formed from at least two different materials. In a specific embodiment, forming multi-layer blocking dielectric region 724 from at least two different materials includes oxidizing a top portion of charge-trapping layer 722 and, subsequently, depositing a dielectric layer above the oxidized portion of charge-trapping layer 724. In another specific embodiment, forming multi-layer blocking dielectric region 724 from at least two different materials includes depositing a first dielectric layer having a first dielectric constant and, subsequently, depositing a second dielectric layer having a second dielectric constant, wherein the second dielectric constant is greater than the first dielectric constant.

Referring to FIG. 7E, a gate layer 730 is formed on the top surface of multi-layer blocking dielectric region 724. Gate layer 730 may be formed from any material and from any process described in association with gate layer 504D from FIG. 5. Thus, a gate stack 732 may be formed above substrate 702.

Referring to FIG. 7F, gate stack 732 is patterned to form a patterned gate stack 704 above substrate 702. Patterned gate stack 704 includes a patterned tunnel dielectric layer 704A, a patterned charge-trapping layer 704B, a patterned multi-layer blocking dielectric region 704C, and a patterned gate layer 704D. Patterned multi-layer blocking dielectric region 704C includes a patterned first dielectric layer 706 and a patterned second dielectric layer 708. Gate stack 732 may be patterned to form patterned gate stack 704 by any process suitable to provide substantially vertical sidewalls for gate stack 704 with high selectivity to substrate 702. In accordance with an embodiment of the present invention, gate stack 732 is patterned to form patterned gate stack 704 by a lithography and etch process. In a specific embodiment, the etch process is an anisotropic etch process utilizing gases such as, but not limited to, carbon tetrafluoride (CF₄), 02, hydrogen bromide (HBr) and chlorine (Cl₂).

Referring to FIG. 7G, it may be desirable to implant dopant impurity atoms 740 into the exposed portions of substrate 704 to form source and drain tip extension regions 750. Source and drain tip extension regions 750 will ultimately become part of source and drain regions formed subsequently, as described below. Thus, by forming source and drain tip extension regions 750 as defined by the location of patterned gate stack 704, channel region 712 may be defined, as depicted in FIG. 7G. In one embodiment, the conductivity type and the concentration of dopant impurity atoms used to form source and drain tip extension regions 750 are substantially the same as those used to form source and drain regions, described below.

Referring to FIG. 7H, it may be desirable to form a pair of dielectric spacers 714 on the sidewalls of patterned gate stack 704, as is well-known in the art. Finally, referring to FIG. 7I, source and drain regions 710 are formed by implanting dopant impurity atoms 760 into the exposed portions of substrate 704. Source and drain regions 710 may have any characteristics as those described in association with source and drain regions 510 from FIG. 5. In accordance with an embodiment of the present invention, the profile of source and drain regions 710 is defined by dielectric spacers 714, patterned gate stack 704 and source and drain tip extension regions 750, as depicted in FIG. 7I.

In another embodiment, a nonvolatile charge trap memory device is fabricated to include a graded blocking dielectric layer. FIGS. 8A-8C illustrate cross-sectional views representing operations in the formation of a nonvolatile charge trap memory device having a graded high dielectric constant blocking layer, in accordance with an embodiment of the present invention.

Referring to FIG. 8A, a charge-trapping layer 822 and a tunnel dielectric layer 820, formed on the top surface of a substrate 802, are provided. Substrate 802 may be composed of any material and have any characteristics described in association with substrate 602 from FIG. 6. Charge-trapping layer 822 and tunnel dielectric layer 820 may be formed from any material, from any process, and have any thickness described in association with charge-trapping layer 604B and tunnel dielectric layer 604A, respectively, from FIG. 6.

Referring to FIG. 8B, a graded blocking dielectric layer 824 is formed on the top surface of charge-trapping layer 822. In accordance with an embodiment of the present invention, graded blocking dielectric layer 824 is formed directly above charge-trapping layer 822, as depicted in FIG. 8B. In one embodiment, graded blocking dielectric layer 824 has a low-to-high gradient in the direction from charge-trapping layer 822 to the top surface of graded blocking dielectric layer 824. Graded blocking dielectric layer 824 may be formed by any technique, composed of any materials, and have any thicknesses described in association with graded blocking dielectric layer 604C from FIG. 6. In accordance with an embodiment of the present invention, there is no distinct interface within graded blocking dielectric layer 824, as depicted in FIG. 8B. In one embodiment, graded blocking dielectric layer 824 is formed from at least two different materials. In a specific embodiment, forming graded blocking dielectric layer 824 from at least two different materials includes oxidizing a top portion of charge-trapping layer 822 and, subsequently, depositing a dielectric layer above the oxidized portion of charge-trapping layer 824. In another specific embodiment, forming graded blocking dielectric layer 824 from at least two different materials includes depositing a first dielectric layer having a first dielectric constant and, subsequently, depositing a second dielectric layer having a second dielectric constant, wherein the second dielectric constant is greater than the first dielectric constant.

Referring to FIG. 8C, process steps similar to those described in association with FIGS. 7E-7I are carried out to form a nonvolatile charge trap memory device having a graded blocking dielectric layer. Thus, a patterned gate stack 804 is formed over a substrate 802. Source and drain regions 810 are formed on either side of patterned gate stack 804, defining a channel region 812. Patterned gate stack 804 includes a patterned tunnel dielectric layer 804A, a patterned charge-trapping layer 704B, a patterned graded blocking dielectric layer 804C and a patterned gate layer 804D.

Thus, nonvolatile charge trap memory devices have been disclosed. The devices each include a substrate having a channel region and a pair of source and drain regions. A gate stack is above the substrate over the channel region and between the pair of source and drain regions. In accordance with an embodiment of the present invention, the gate stack includes a high dielectric constant blocking region. In one embodiment, the high dielectric constant blocking region is a bi-layer blocking dielectric region. In another embodiment, the high dielectric constant blocking region is a graded blocking dielectric layer. 

1. A nonvolatile charge trap memory device, comprising: a substrate having a channel region, a source region and a drain region; and a gate stack disposed above the substrate over the channel region and between the source region and the drain region, wherein the gate stack comprises a multi-layer blocking dielectric region.
 2. The nonvolatile charge trap memory device of claim 1, wherein the nonvolatile charge trap memory device is a SONOS-type device, the gate stack further comprising: a tunnel dielectric layer disposed above the channel region; a charge-trapping layer disposed above the tunnel dielectric layer and below the multi-layer blocking dielectric region; and a gate layer disposed above the multi-layer blocking dielectric region.
 3. The nonvolatile charge trap memory device of claim 2, wherein the multi-layer blocking dielectric region is a bi-layer blocking dielectric region having a first dielectric layer disposed directly above the charge-trapping layer and a second dielectric layer disposed directly above the first dielectric layer and directly below the gate layer, and wherein the dielectric constant of the first dielectric layer is lower than the dielectric constant of the second dielectric layer.
 4. The nonvolatile charge trap memory device of claim 2, wherein the multi-layer blocking dielectric region is a bi-layer blocking dielectric region having a first dielectric layer disposed directly above the charge-trapping layer and a second dielectric layer disposed directly above the first dielectric layer and directly below the gate layer, wherein the first dielectric layer has a large barrier height, and wherein the second dielectric layer has a high dielectric constant.
 5. The nonvolatile charge trap memory device of claim 3, wherein the first dielectric layer of the bi-layer blocking dielectric region comprises silicon dioxide, and wherein the second dielectric layer of the bi-layer blocking dielectric region comprises a material selected from the group consisting of silicon nitride, aluminum oxide, hafnium oxide, zirconium oxide, hafnium silicate, zirconium silicate, hafnium oxy-nitride, hafnium zirconium oxide and lanthanum oxide.
 6. The nonvolatile charge trap memory device of claim 3, wherein the first dielectric layer of the bi-layer blocking dielectric region comprises a material having a dielectric constant approximately in the range of 3.5-4.5, and wherein the second dielectric layer of the bi-layer blocking dielectric region comprises a material having a dielectric constant above approximately
 7. 7. The nonvolatile charge trap memory device of claim 2, wherein the tunnel dielectric layer comprises a high-K dielectric portion, wherein the charge-trapping layer comprises a bi-layer silicon oxy-nitride region, and wherein the gate layer is a high work-function gate layer.
 8. A nonvolatile charge trap memory device, comprising: a substrate having a channel region, a source region and a drain region; and a gate stack disposed above the substrate over the channel region and between the source region and the drain region, wherein the gate stack comprises a graded blocking dielectric layer.
 9. The nonvolatile charge trap memory device of claim 8, wherein the nonvolatile charge trap memory device is a SONOS-type device, the gate stack further comprising; a tunnel dielectric layer disposed above the channel region; a charge-trapping layer disposed above the tunnel dielectric layer and below the graded blocking dielectric layer; and a gate layer disposed above the graded blocking dielectric layer.
 10. The nonvolatile charge trap memory device of claim 9, wherein the graded blocking dielectric layer is disposed directly above the charge-trapping layer and directly below the gate layer, and wherein the dielectric constant of the graded blocking dielectric layer has a low-to-high gradient in the direction from the charge-trapping layer to the gate layer.
 11. The nonvolatile charge trap memory device of claim 10, wherein the portion of the graded blocking dielectric layer directly adjacent to the charge-trapping layer consists essentially of silicon dioxide, and wherein the portion of the graded blocking dielectric layer directly adjacent to the gate layer consists essentially of silicon nitride.
 12. The nonvolatile charge trap memory device of claim 10, wherein the portion of the graded blocking dielectric layer directly adjacent to the charge-trapping layer consists essentially of silicon dioxide, and wherein the portion of the graded blocking dielectric layer directly adjacent to the gate layer consists essentially of a material selected from the group consisting of aluminum oxide, hafnium oxide, zirconium oxide, hafnium silicate, zirconium silicate, hafnium oxy-nitride, hafnium zirconium oxide and lanthanum oxide.
 13. The nonvolatile charge trap memory device of claim 10, wherein the portion of the graded blocking dielectric layer directly adjacent to the charge-trapping layer consists essentially of a material having a dielectric constant approximately in the range of 3.5-4.5, and wherein the portion of the graded blocking dielectric layer directly adjacent to the gate layer consists essentially of a material having a dielectric constant above approximately
 7. 14. The nonvolatile charge trap memory device of claim 9, wherein the tunnel dielectric layer comprises a high-K dielectric portion, wherein the charge-trapping layer comprises a bi-layer silicon oxy-nitride region, and wherein the gate layer is a high work-function gate layer.
 15. A method of fabricating a nonvolatile charge trap memory device, comprising: providing a substrate; forming a gate stack above the substrate, wherein forming the gate stack comprises: forming a tunnel dielectric layer above the substrate; forming a charge-trapping layer above the tunnel dielectric layer; forming a blocking dielectric region above the charge-trapping layer, wherein the blocking dielectric region is formed from at least two different materials; forming a gate layer above the blocking dielectric region; and patterning the tunnel dielectric layer, the charge-trapping layer, the blocking dielectric region, and the gate layer; and forming a source region and a drain region in the substrate and on other side of the gate stack to provide a channel region in the substrate and below the gate stack.
 16. The method of claim 15, wherein forming the blocking dielectric region from at least two different materials comprises oxidizing a top portion of the charge-trapping layer and, subsequently, depositing a dielectric layer above the oxidized portion of the charge-trapping layer.
 17. The method of claim 15, wherein forming the blocking dielectric region from at least two different materials comprises depositing a first dielectric layer having a first dielectric constant and, subsequently, depositing a second dielectric layer having a second dielectric constant.
 18. The method of claim 17, wherein the second dielectric constant is greater than the first dielectric constant.
 19. The method of claim 15, wherein the blocking dielectric region is a bi-layer blocking dielectric region having a first dielectric layer disposed directly above the charge-trapping layer and a second dielectric layer disposed directly above the first dielectric layer and directly below the gate layer, and wherein the dielectric constant of the first dielectric layer is lower than the dielectric constant of the second dielectric layer.
 20. The method of claim 15, wherein the blocking dielectric region is a graded blocking dielectric layer disposed directly above the charge-trapping layer and directly below the gate layer, and wherein the dielectric constant of the graded blocking dielectric layer has a low-to-high gradient in the direction from the charge-trapping layer to the gate layer. 